The present invention relates generally to analog-to-digital converters and more particularly to analog-to-digital having a tunable frequency response.
Currently, many products use analog-to-digital converter circuits. The reason for this is that microprocessors analyze and use only digital data. Analog-to-digital converters are, therefore, necessary to convert electrical analog data to digital data.
As the need to convert analog data to digital data has increased, analog-to-digital converter circuits have become more sophisticated. Typical analog-to-digital converter circuits are no longer comprised of individual discrete components, but are instead comprised of integrated circuits and are capable of greater speed, resolution and accuracy.
A typical high-speed high-performance analog-to-digital converter has several components. These components include a track and hold circuit for sampling the analog input at a given clock rate, a large number of amplifiers for amplifying the input signal, a comparator to detect the level of the amplified signal and an encoder to convert the signal to a digital output. The accuracy of the analog-to-digital circuit is directly related to matching the gain and frequency response of the amplifiers to the clock rate and the comparator.
Unfortunately, it is hard to predict the performance of integrated circuits with accuracy, particularly mixed (digital and analog) signal integrated circuits that lack precision models for interconnection parasitic losses. The problem can increase due to intrinsic process variations within each integrated circuit wafer, from wafer-to-wafer, and lot-to-lot. It would, therefore, be desirable to fabricate each integrated circuit amplifier with the correct frequency response.
Matching the gain and frequency response to the clock rate and the comparator, however, can be quite difficult in an integrated circuit, particularly since they are difficult to modify after the fabrication process. Also, as the sampling frequency is increased, an incorrect amplifier frequency response will have a proportionately larger impact on overall accuracy. In satellite communication applications, typical sampling frequencies are in the multi-gigahertz range. Therefore, if the frequency response could be tuned after the integrated circuit was fabricated, many of the above issues could be solved.
It is, therefore, an object of the invention to provide an improved and reliable analog-to-digital converter circuit. Another object of the invention is to provide an analog-to-digital converter circuit with an adjustable gain and frequency response.
In one aspect of the invention, a circuit includes an analog-to-digital converter. The analog-to-digital converter has an amplifier circuit whose gain and frequency response are controlled by a varactor control circuit.
In a further aspect of the invention, an analog-to-digital converter is used to convert an analog signal to a digital signal. A track and hold core circuit samples and holds the analog signal at a predetermined clock frequency to generate a sampled analog signal. A track and hold buffer circuit then amplifies the sampled analog signal by an amount enhanced by a first varactor control circuit to produce a first amplified signal. Two or more preamplifier circuits further amplify the first amplified analog signal by an amount enhanced by a second varactor control circuit to produce a second amplified signal. The level of the second amplified signal is then determined by a comparator and converted to a binary output by an encoder.
The present invention thus achieves an improved analog-to-digital converter circuit with an adjustable gain and frequency response. The present invention is advantageous in that it improves circuit performance while increasing the overall production yield when compared to conventional technology.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.